Report on VHS in wrasse

Siri Elise Dybdal

According to the report, an outbreak of Viral Haemorrhagic Septicaemia (VHS) was detected during December 2012 in multiple species of wrasse (Labridae) stocked onto six sea-water sites around Shetland mainland.

The wrasse were originally captured from the wild off the west coast of the Scottish mainland and were being used as a biological control of sea-lice on Atlantic salmon farms.

Inspection, diagnostic testing, contact tracing, epidemiological enquires and other relevant research were undertaken as part of an outbreak investigation, containment areas were established, and the removal of stocked wrasse was initiated. To date three of the six affected sites have been cleared with a substantial proportion (˜99%) of wrasse removed from the remaining sites.

Species other than wrasse were also tested for VHS. Lumpsucker and Atlantic salmon stocked on VHS positive sites tested VHS negative. Wild poor cod from within the pens of a VHS positive site tested VHS positive. Free-ranging wild Norway pout, sprat, grey gurnard, herring, whiting and plaice from a locality around Shetland tested VHS positive.

A qualitative risk analysis suggests that the chance of this outbreak originating from the marine environment around Shetland is moderate and alternative possibilities are either low or negligible.